The present invention generally relates to balance compensation of rotational devices, and more particularly relates to compensating for dynamic unbalance of a rotating assembly, especially on a vehicle, such as a spacecraft.
Spacecraft (e.g., satellites) are frequently equipped with one or more spinning assemblies which rotate about an axis of rotation and exhibit a large product of inertia about the axis of rotation. For example, telescopes and other instruments can be mounted on a spinning platform on a spacecraft and rotated relative to the spacecraft. Other examples of rotating assemblies include parabolic antennas and reflectors which are continually rotated on a spinning platform, usually at constant speed relative to the spacecraft. Some rotating assemblies exhibit a static unbalance and/or a dynamic unbalance. A static unbalance is generally an unbalance in a radial direction to the axis of rotation that is characterized as a force that remains fixed in orientation with respect to the body of the rotating assembly. A dynamic unbalance is generally characterized as a moment that is a result of the rotating assembly about an axis other than a principle axis. An asymmetric assembly rotated about an axis, or a symmetric device rotated about an axis other than its principle axis, will generally tend to exhibit a dynamic unbalance moment.
The presence of a dynamic unbalance moment adversely affects stabilization of a spacecraft in orbit by tending to cause the spacecraft to move, e.g., jitter, in response to the rotating moment. Thus, the presence of a dynamic unbalance moment will tend to cause spacecraft pointing error which requires additional stability control to maintain the spacecraft in a desired orientation in orbit. One approach to mitigating dynamic unbalance includes adding balance mass to the rotating assembly in a manner that provides an equal but opposite moment to cancel out the dynamic unbalance moment. However, the addition of balance mass has several drawbacks including added size and weight to the spacecraft. Additionally, allowable envelope constraints may restrict where the balancing mass can be added. Further, if the envelope constraints are severe, the length of the moment arm of the balance mass may have to be reduced, thus resulting in an increase in the balance weights. As a consequence, the balance weights may have to be larger than the mass creating the initial unbalance.
Accordingly, it is therefore desirable to provide for a system which compensates for dynamic unbalance of a rotating assembly on a vehicle, such as a spacecraft, which does not exhibit drawbacks of the known prior approaches. In particular, it is desirable to provide for such a dynamic balanced system which does not add a significant amount of weight to the rotating assembly and meets strict envelope constraints.
The present invention provides a dynamic unbalance compensation system and method that compensates for dynamic unbalance of a rotational assembly. The system advantageously compensates for the dynamic unbalance of the rotational assembly without adding a significant amount of mass to the rotational assembly. The system includes a support member, such as a vehicle, a rotational assembly mounted on the support member and rotatable about an axis of rotation relative to the support member, and a momentum device mounted on the rotational assembly and generating a momentum vector component perpendicular to the axis of rotation. The momentum vector component produces a compensation torque when the rotational assembly rotates such that the compensation torque compensates for dynamic unbalance of the rotational assembly. According to one aspect of the present invention, the system is particularly well-suited for use on a vehicle, such as a spacecraft.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.